1. Field of the Invention
The present invention relates to a lensed fiber assembly wherein an optical fiber is canted at an angle to the axis of light propagation.
2. Description of Related Art
In the field of fiber optic coupling it is desirable to reduce back reflection of an optical interface in an optical system, such as that between an active optical device and a fiber coupled thereto. A known method involves angling the end-face of an optical fiber by a small amount and then angling the emitted beam of, for instance a laser diode, relative to the end-face surface of the optical fiber by a slightly larger amount than the angle of the fiber end-face. The net effect is to have the emitted light reflect off the surface of the fiber end-face at a large total angle, in order to avoid interference with the light energy emitted from the laser diode. Light transmitted through the surface of the fiber is refracted at a known angle, related to the refractive index of the fiber optic material, so as to bend the light as close as possible to the fiber axis, resulting in a light beam which is well-coupled and guided down the fiber core.
Unfortunately, the alignment of the optical fiber with the active optical device is a time and labor intensive process, necessitating illumination of any lenses incorporated in the system with the light from the active optical device and movement of the optical fiber in many directions to find the precise position and angle necessary to optimally couple the light beam into the fiber.
The typical method for performing this geometrical alignment is to align an intermediate optical device, such as a GRIN lens, a ball lens or a hemispherical lens, slightly off-axis to the emitted light energy at the active optical device, thereby inducing an angle between the propagation axis of the light energy at the focussed spot on the far side of the lens and the original emission direction at the emitting surface of the active optical device. This angle is adjusted so the light energy aligns with the core of the optical fiber as described above.
This manner of alignment is complicated by the fact that with each movement along the axis of the emitted light (to peak or optimize the coupling of the emitted light into the fiber) a new lateral position has to be found to regain the light energy coupling. In an automated alignment system, the equipment has to make many corrections to the lateral position when optimizing the axial position so that the equipment can tell if the new axial position is indeed in an improved coupled position.
Ishizuka et al., U.S. Pat. No. 5,087,109, discloses a method for coupling a semiconductor laser with an optical fiber wherein the position of the semiconductor laser is deviated from the axis of the coupling lens by a value corresponding to the inclination angle of the optical fiber input end face, or the semiconductor laser is inclined. The Ishizuka et al. method is essentially the same as that described above.
U.S. Pat. No. 4,831,882 to Sabine discloses a termination for optical light guides which can be integrally formed at the ends of long light guides or attached as discrete termination pieces. A polarized light source is directed at an angle to the optical waveguide axis, similar to the above-described method. U.S. Pat. No. 4,695,126, discloses a method and apparatus for effecting light energy transmission with lessened reflection, wherein an optical fiber assembly has an inclined passage between end openings for residence of an optical fiber.
The disclosures of the above-cited references are incorporated by reference herein.